Conduits, such as copper tubing are well known in plumbing applications where the tubing is used for channeling liquids from a first location to a second location. Copper conduit is assembled from various sections of curved as well as straight pieces of tubing. The pieces of tubing, also referred to as profiles, particularly when the pieces are non-circular in cross-section, are cut to length and soldered together with fittings, e.g., elbows, shutoff valves, and/or tees, in a desired configuration. However, the assembly process is labor intensive. Moreover, the cost of copper is substantial and in recent times has dramatically increased. Additionally, the welding process typically requires more welding knowledge than the average do-it-yourself plumber possesses.
To compensate, at least in part, for the rise in production costs, producers of plumbing supplies have turned to forming conduit from polymeric materials. In particular, polyvinyl chloride (“PVC”) and polyethylene (“PE”) are commonly used to construct plumbing conduit, as well as fittings and valves. Polymeric materials are often connected by using adhesives to connect the joints together. The adhesive is considerably easier to apply than solder, which may simplify the profile assembly process.
In certain applications, the plumbing conduit must follow a circuitous path, for example, through walls in a structure or around components in a machine or appliance. When profiles are connected using adhesives, leaks may occur at the joints. The increase in connections between sections of tubing may lead to an increased potential for leaks within the system. Solutions intent on obviating these problems focus on forming conduits as a unitary article by injection overmolding.
Injection overmolding of thermoplastics is a process by which plastic is melted and injected into a mold cavity void. Once the melted plastic is in the mold void volume, it cools to a shape that reflects the geometry of the void. When polymers are heated in an injection molding operation, they soften and as pressure is applied, flow through the runners in the mold into the mold cavity or cavities. The mold has cavities that, when filled with the polymeric material, define the overmolded part. During the overmolding process a core pin is inserted into the cavity to form a channel through the overmolded part. As the polymeric material cools, the material hardens. When cooled enough, the mold is opened and the overmolded part is removed.
Conventional core pins are used in plastic injection overmolding processes when channels are desired in the overmolded part. In order to accomplish this function the core pin projects into the cavity and prevents the plastic from filling the area occupied by the core pin. If a channel is desired completely through the overmolded part the core pin must seat tightly against the opposing face of the mold or project into an inserted profile. The core pin is the accepted means of accomplishing this task. However, inasmuch as the core pin is typically a fixed length of a generally straight configuration when mounted in the mold there are certain limitations, particularly when it is used to form a channel completely through a rigid curved overmolded part.
During a linear overmolding process, melted polymer material flows into and around the other preformed element(s) (e.g., a core pin or insert, which may be a polymer which is able to withstand elevated temperatures within the mold without significant deformation, or more typically will be metallic in composition, and/or inserted polymer tube(s)). A straight core pin is easily inserted into the mold cavity and easily removed from any polymer overmolded part.
In a non-linear, i.e., curved overmolding operation, when the overmolded polymeric material is flexible, the core pin may be removed from the overmolded section of the part by simply moving the core pin out of axial alignment with the overmold and the flexibility of the overmold accommodates removal of the core pin.
In the current state of the art, for rigid or semi-rigid polymers, the application of overmolding is limited primarily to linear profiles. Thus, to assemble a non-linear conduit made from a rigid polymer, traditional adhesives are used to connect linear and non-linear sections of tubing. There exists a need for an overmolding process to form non-linear overmolded sections having a radius of curvature (Rc) from substantially rigid polymers.
In this invention, the problem of overmolding non-linear sections of rigid or semi-rigid polymers is solved by incorporating a core pin having a radius of curvature corresponding to the desired overmold final configuration so that a non-linear overmold may be constructed without the use of adhesives. The result is an overmold having a hollow interior channel corresponding to the radius of the curvature of the core pin.